The gas-phase manufacture of titanium dioxide is subject to acute fouling in the cooler unit located directly downstream of the reactor which quenches the reaction. A model of the cooler system was constructed, incorporating aspects of compressible flow, multimode heat transfer, fouling, and changes in geometry. This indicated that deposition could be very rapid. The effect of deposit layer buildup required measurement of the thermal conductivity of the porous layer; this was achieved using a novel testing device similar to that reported by Tan et al. (2006), for measuring the thermal conductivity of surface coatings. Active mitigation techniques are employed to reduce the effect of rapid fouling. The effectiveness of adding an erodent, in this case sand, to the flow was appraised by studying the breakup of deposit layers by impinging particles. The experimental conditions (high-temperature chlorine gas, high flow velocities) were simulated in cold experiments by matching the inertia and size of test particles to those of the sand. These studies showed that sand at the feed size would detach deposits, but could result in breakage of the sand particles. Mitigation efficiency is then determined by sand distribution and redistribution.